In a Small Moment: Cheating and Class Size in Italian Primary Schools ⇤

Using a Maimonides-Rule identification strategy based on class-size cutoffs around 25, we document a payoff to smaller classes in Italian primary schools. These gains are driven mainly by schools in Southern Italy, suggesting a substantial return to class size for relatively poor residents of the Mezzogiorno. In addition to low SES, however, the Mezzogiorno is distinguished by pervasive teacher cheating on standardized tests, a fact established by an experiment randomly assigning school monitors. We use Italy’s Maimonides Rule to show that small classes facilitate teacher cheating, providing an alternative explanation for the causal effects of class size on test scores in Southern Italy. This motivates a causal model for achievement with two endogenous variables, class size and proportion cheating. The model is identified by a combination of class size cutoffs and randomly assigned classroom monitors. The resulting estimates suggest that the effects of class size on measured achievement in Italian primary schools are driven entirely by the relationship between class size and teacher cheating. Models that estimate class size and cheating effects jointly generate precise zeros for the former.